/Engine/Source/Runtime/Core/Public/Math/UnrealMathUtility.h
InOutScissorRect should be set to View.ViewRect before the call
0: light is not visible, 1:use scissor rect, 2: no scissor rect needed
static uint32 ComputeProjectedSphereScissorRect ( FIntRect & InOutScissorRect, FVector SphereOrigin, float Radius, FVector ViewOrigin, const FMatrix & ViewMatrix, const FMatrix & ProjMatrix )